The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut [1890] at sacred-texts.com

17. And on account of the settled meaning.

The small ether within cannot denote anything but the highest Lord for this reason also, that the word 'ether' has (among other meanings) the settled meaning of 'highest Lord.' Compare, for instance, the sense in which the word 'ether' is used in Kh. Up. VIII, 14, 'He who is called ether is the revealer of all forms and names;' and Kh. Up. I, 9, 1, 'All these beings take their rise from the ether,' &c. On the other hand, we do not meet with any passage in which the word 'ether' is used in the sense of 'individual soul.'--We have already shown that the word cannot, in our passage, denote the elemental ether; for, although the word certainly has that settled meaning, it cannot have it here, because the elemental ether cannot possibly be compared to itself, &c. &c.